The proposed research will examine vocal development in infant vervet monkeys. Specifically, the mechanisms that guide development in the production, usage, and comprehension of vocalizations will be investigated. These findings will directly benefit the study of the vervet system and inform investigations of human communication and language development. The vervet system is an especially good model for human vocal communication development because the two systems share complex developmental changes over vocal production, usage, and comprehension, and they are phylogenetically related. The first goal is to characterize the vocal communication system of infant vervet monkeys in a laboratory colony. These lab observations will extend field observations that demonstrated complex changes during the development of the vervets' vocal production, usage, and comprehension. Acoustic analyses of the vocalizations and an ethogram of the vervets' behaviors will be combined to provide a full description of changes in the vocal communication system. The second goal is to determine how internal constraints interact with social and vocal experience to guide the infant vervets' vocal communication development. Several established procedures will be used to investigate the initial constraints on the infant vervets' vocal communication system, as well as the influences of social and vocal experience. Combining experimental manipulations with detailed observations of spontaneous behavior will provide a thorough study of the changes in infant vervets' vocal communication system.